Recently, the improvement of the processing performance of the computer system has been anxiously hoped for, among others, that of the I/O processing performance of the disk subsystem thereof being in high demand. The I/O performance of the disk subsystem (hereinafter, referred to as “subsystem”) that uses a magnetic disc as memory medium is inferior in the order of three to four digits to that of the main memory of a computer incorporating a semiconductor memory unit as a memory medium. Thus, the utmost efforts have been made to date to make the I/O processing performance of the subsystem closer to that of the main memory of the computer.
There is general tendency among such large enterprises as banking facilities, security and telecommunication companies to reduce costs related to the operation, maintenance and control of the computer and storage systems by centralizing computer and storage units that have been dispersedly disposed in the past into a data center so as to systematize the above units. Thus, in particular, for a large-scale and high-end storage system, such support systems are required as channel interfaces for connecting the same system to several hundreds of host computers for network connectivity and upgraded memory capacity of several hundred terabytes or more.
On the other hand, the enlargement of the open systems market in recent years and the yet to come prevailing of the storage area network (SAN) unavoidably requires a small-scale storage system (of miniature size) having the same high function and credibility as the large-scale and high-end storage system as mentioned above.
As a method for improving the I/O processing performance of the subsystem, a so-called disk array system is known wherein the subsystem comprises the plurality of magnetic disc units, into which disc units data are stored. This system generally comprises the plurality of magnetic disc units to record the I/O data from the higher order computer and a disk array controller to receive the I/O data from the computer and to transfer the same to the plurality of magnetic disc units. For the large-scale network connection and the large volume of communication, it may be arranged such that an ultra large-scale disk array controller is set up by connecting the plurality of disk array controllers of the conventional large-scale and high-end type. The connection of the plurality of disk array controllers allows cache memory to be dispersed into the respective controllers. For the performance's sake, it is advantageous that the cache memory stores the data of the magnetic disc units connected to the storage controller while the host computer getting access to the cache memory is connected to the storage controller having the same memory. However, the happening of packaging faults and the additional installation of the magnetic disc units and the storage controllers may cause the correspondence between the host interface section and the cache memory as well as between the cache memory and the magnetic disc controllers to alter from the above advantageous arrangements. Seen from the higher order apparatus and software systems as well as viewed from the conventional architectural continuation, it is advantageous that management is directed for the sole disk array controller rather than for an ultra large-scale disk array controller connecting the plurality of disk array controlling units. Restructuring caused by the connection of the host interface with the cache memory and the magnetic disc units or the additional installation thereof requires the packaging positions thereof to be optimized, which affects the performance of the disk array system more significantly than in the prior case where the system has been constructed by the sole disk array controller.
For instances, the prior disk array controller as shown in FIG. 2 is provided with the plurality of channel interface sections 11 to execute the data transfer between the host computer 50 and the disk array controllers 2, the plurality of the disc interface sections 12 to execute the data transfer between the magnetic disc units 5 and the disk array controllers 2 and the cache memory sections 14 to temporarily store the data of the magnetic disc units 5, wherein the cache memory sections 14 are accessible from all the channel interface sections 11 and the disc interface sections 12 within one disk array controller 2. In this disk array controller 2, a mutual connection network 21 intervenes between the channel interface section 11 and the cache memory section 14.
The channel interface section 11 is provided with an interface to connect with the host computer 50 and a microprocessor, which is not shown in the drawing, to control the input and output data of the host computer 50, while the disc interface section 12 is provided with an interface to connect with the magnetic disc unit 5 and a microprocessor, which is not shown in the drawing, to control the input and output data of the magnetic disc unit 5. The disc interface section 12 performs the execution of the RAID function as well.
Where it is required to store the data more than that stored in the sole disk array controller 2 in this prior art, the plurality of disk array controllers 2 are set up, to which controllers channels are connected from the host computer 50.
Where a host computer 50 having the number of host channels more than that of those connectable to the sole disk array controller 2 is arranged for connection, the plurality of disk array controllers 2 are set up, to the respective of which controllers the host computer 50 is connected.
Where the data are transferred among the plurality of the disk array controllers 2, channels are connected to two disk array controllers 2 performing the data transfer from the sole host computer 50, through which computer the data are transferred therebetween.
Another prior disk array controller as shown in FIG. 3 is provided with a host computer 50, disk array controllers 2, an external connection network 23 intervening between the host computer 50 and the disk array controllers, the plurality of channel interface sections 11 to execute the data transfer between the host computer 50 and the disk array controllers 2, the plurality of disc interface sections 12 to execute the data transfer between the magnetic disc units 5 and the disk array controllers 2 and the cache memory sections 14 to temporarily store the data of the magnetic disc units 5, wherein the host computer 50 is through the external connection network 23 accessible to all the disk array controllers 2 and it is arranged such that the cache memory sections 14 are accessible from all the channel interface sections 11 and the disc interface sections 12 within the sole disk array controller 2. In this prior art, a mutual connection network 21 intervenes between the interface sections 11 and 12 and the cache memory sections 14.
The channel interface section 11 is provided with an interface to connect with the host computer 50 and a microprocessor, which is not shown in the drawing, to control the input and output data of the host computer 50 while the disc interface section 12 is provided with an interface to connect with the magnetic disc unit 5 and a microprocessor, which is not shown in the drawing, to control the input and output data of the magnetic disc unit 5. The interface section 12 also performs the execution of the RAID function.